1. Field of the Invention
The invention relates to digital magnetic read/write transducers particularly with respect to perpendicular magnetic recording on a moving magnetic medium.
2. Description of the Prior Art
Digital magnetic storage systems are in use in which a recording and reading head adjacent a moving magnetic medium magnetizes small areas on the medium for recording digital data and senses the magnetized areas for reading the data. To date the only commercially practicable type of system has been the longitudinal magnetic recording arrangement. Longitudinal magnetic recording utilizes a ring-type head comprising a ring shaped core of high permeability material with a narrow gap therein disposed above or below the moving magnetic medium with the gap length disposed parallel to the direction of travel of the medium. A current pulse applied to a coil wound on the core generates flux lines within the core that are completed along a path comprising one edge of the gap, the magnetic medium adjacent the gap and the other edge of the gap. The flux polarity so threading the medium effects the recording of data. To read the data when the magnetized area on the medium passes adjacent the gap, a flux path through the core is established, thereby threading the coil with flux lines generating a signal indicative of the recorded information.
Such longitudinal magnetic recording systems suffer from the disadvantage of the limited linear bit density that is supportable by the medium. This basic limitation occurs because the magnetized domains in the medium are longitudinally oriented with respect to the medium. This mode exhibits a maximum demagnetizing field at the bit boundary thus limiting the number of transitions that can be recorded in each lineal inch along the recording track. Present practical longitudinal magnetic recording systems also suffer from the disadvantage that the recording and reading gap in the transducer is of a dimension that is a compromise between the reading and writing requirements. Generally a wide gap is desired for writing whereas a narrow gap is desired for reading. The compromised dimension of the gap utilized for both reading and writing results in a degradation in performance with respect to what optimally would be possible in each of the reading and writing modes of the system.
In order to attain a substantial higher lineal bit density than that provided by longitudinal magnetic recording, perpendicular mode magnetic recording may be utilized. In perpendicular magnetic recording, magnetic flux is directed perpendicularly through the medium rather than longitudinally along the medium, as in longitudinal magnetic recording, to effect magnetic domains oriented perpendicular to the surface of the medium. This mode exhibits a minimum demagnetizing field at the bit boundary and thus a larger number of perpendicularly oriented transitions can be packed into each lineal inch of the medium as compared to that of longitudinal magnetic recording systems.
It is appreciated, therefore, that perpendicular magnetic recording offers the potential of greater lineal packing density than does longitudinal magnetic recording. Longitudinal magnetic recording is, however, in wide spread commercial usage whereas perpendicular magnetic recording is, to date, merely a laboratory curiosity. It is believed that perpendicular magnetic recording has not as yet been rendered commercially practicable because of the lack of a suitable read/write transducer compatible with present day magnetic storage interface arrangements. Heretofore an isolated recording pole disposed perpendicular to the medium and a similar pole collinearly disposed beneath the medium with respect to the first pole have provided the perpendicular magnetic recording flux through the medium so as to effect the desired perpendicular orientation of the magnetic domains. The flux return path for such an arrangement is either through the air and/or through the drive spindle and medium substrate of the system. Such arrangements are exceedingly inefficient magnetically and only provide the write function. A separate read head would then be required. Such arrangements are incompatible with present day multiple head, multiple track mass storage systems utilizing one head for both READ and WRITE, rendering the use thereof commercially impracticable.